Middle Miocene greenhouse and cooling: the deep North Atlantic Ocean record

中新世温室和降温：北大西洋深处的记录

• 批准号: NE/Y001699/1
• 负责人: Sevasti Modestou
• 金额: $ 2.08万
• 依托单位: Northumbria University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FY001699%2F1
• 关键词: Middle; Miocene; greenhouse; cooling; deep

Nearly everyone in our society is aware that human activity has increased the concentration of carbon dioxide in the atmosphere, leading to warming. What is not common knowledge is that the last time Earth's CO2 levels were as high as predicted for the near future was about 16 million years ago, during the middle Miocene Climatic Optimum. This period was a time of significant global change, including extensive volcanism leading to the high CO2, warmer 'climate optimum', later followed by significant drops in CO2 linked with cooling. Consequently, studying the climate of the middle Miocene will provide baseline information required to understand the effects of the expected future CO2-driven global warming. This information can in turn help inform policy makers on ways to mitigate and adapt to climate change. My research will apply a proxy known as 'clumped isotopes' in fossils to determine deep sea and sea surface temperatures in the Atlantic Ocean during the middle Miocene. This proxy is a direct palaeothermometer: unlike other available options, the "clumped" isotope composition we can measure from ancient fossils is directly controlled by the temperature the fossils initially grew in. Clumped isotope palaeotemperature measurements also allow us to estimate deep water oxygen isotope compositions without the need to make assumptions, as would be necessary with alternative proxies. Such estimates are a key component for estimating global ice volume, enabling our understanding of how much Earth's ice sheets were impacted by warming climate at that time. Since we do not currently have global coverage for deep sea oxygen isotope compositions during the middle Miocene, we are currently unable to decipher whether the signal observed so far is a true global ice volume signature, or whether other processes are at play. Finally, the clumped isotope method avoids known issues with the only alternative deep water temperature proxy (Mg/Ca ratios), as the "clumping" signature is not impacted by changes in the carbonate ion concentration of seawater; this fundamental property changes significantly with changing atmospheric CO2, and has been observed to impact Mg/Ca ratios during the middle Miocene.The location where we will recover sediment during Exp 395 is crucial for other fundamental earth system mechanisms which exert large influences on climate. Ocean circulation in the North Atlantic is a key component of the climate system today; unfortunately, deep sea sediments as old as the middle Miocene have rarely been recovered in this area, so it has been impossible to examine whether North Atlantic circulation was different during that critical period of climate change. IODP Expedition 395 will recover suitably old and continuous sediments from this region of the North Atlantic for the first time, providing us with an exciting opportunity to discover, compare and contrast the changes that took place in the North Atlantic with elsewhere. This information is critical for placing the temperature and deep sea oxygen isotope composition changes into context within our current climate paradigm.

我们社会中的几乎每个人都知道，人类活动增加了大气中二氧化碳的浓度，从而导致变暖。并不常见的是，在中新世中期气候最佳期间，地球上一次地球的二氧化碳水平与不久的将来所预测的一样高。这一时期是一个发生重大变化的时期，包括广泛的火山，导致高二氧化碳，较温暖的“气候最佳”，然后在与冷却有关的二氧化碳中大幅下降。因此，研究中新世中新世的气候将提供理解预期未来CO2驱动的全球变暖的影响所需的基线信息。此信息反过来可以帮助政策制定者减轻和适应气候变化的方法。我的研究将在中新世期间在大西洋中确定大西洋中的深海和海面温度，以确定化石中的“集结同位素”的代理。该代理是直接的古热量计：与其他可用选项不同，我们可以从古代化石中测量的“结块”同位素组成直接受到化石最初越来越高的温度来控制。在不需要的是不需要的情况下，化石结块的同位素古温晶格测量也使我们可以估算不需要的深水氧气组合物，而不需要做出估计。这样的估计是估计全球冰量的关键组成部分，使我们能够理解当时的地球冰盖受到变暖的气候影响。由于中新世期间我们目前没有全球对深海氧同位素组成的覆盖范围，因此我们目前无法破译到目前为止观察到的信号是否是真正的全球冰量签名，还是其他过程是否在发挥作用。最后，结块的同位素方法避免了唯一的替代深水温度代理（mg/ca比）的已知问题，因为“集结”签名不会受到海水碳酸盐离子浓度的变化的影响；随着大气二氧化碳的变化，这种基本特性发生了显着变化，并且已经观察到在中新世中期会影响Mg/CA的比率。在EXP 395期间我们将恢复沉积物的位置对于其他基本的地球系统机制至关重要，这些机制对气候造成很大影响。北大西洋的海洋循环是当今气候系统的关键组成部分。不幸的是，该地区很少回收像中新世中期一样古老的深海沉积物，因此在气候变化的关键时期，不可能检查北大西洋循环是否有所不同。 IODP Expedition 395将首次从北大西洋地区恢复适当的旧且连续的沉积物，为我们提供了一个令人兴奋的机会，可以发现，比较和对比北大西洋与其他地方发生的变化。该信息对于将温度和深海氧同位素组成变化为我们当前气候范式内的上下文至关重要。